One form of timing belt utilizes a looped belt body provided with a plurality of longitudinally spaced teeth for maintaining accurate relationship between toothed pulleys engaged with the teeth at different portions of the system.
In one form of timing belt, teeth are provided on both the upper and lower surface of the belt.
One such double-toothed belt is illustrated in Japanese Patent Publication No. 22,101/1971. As shown therein, the belt is formed by sequentially winding on a mold a canvas layer, a tensile rope, a nonvulcanized rubber layer, and a second canvas layer. The layers are wound about a mold provided with grooves corresponding to the desired teeth of the belt. A basic mold of rubber having cylindrical grooves is applied to the outer surface of the laminate and pressure vulcanizing thereof is effected so as to extrude the rubber into the grooves of both the inner and outer molds, thereby forming the desired upper and lower teeth.
Another method utilized in the background art is disclosed in the laid open Japanese Patent Application 135056/1974. As disclosed therein, a number of rubber sheets are molded to the spirally wound tensile cords. The method shown therein is similar to the method of Japanese Patent No. 22101, in that each utilizes basic molds to mold the upper teeth, whereby the positions of the upper and lower teeth may be displaced. Not only is there the possibility of providing an irregular array of the teeth, but also it is extremely difficult to equalize the pitch line difference of the upper and lower teeth.